Simplify your PCB layout - When 2 is better than 6


A key contributor to the cost of any electronic product is the number of layers used for the printed circuit board (PCB). An integrated circuit (IC) pin out arrangement optimized for PCB layout will help reduce end product cost.

For example, the TPS23861 4-Port, Type 2, IEEE 802.3at Power Sourcing Equipment (PSE) Controller does exactly that. Plus, the TPS23861 evaluation module (TPS23861EVM-612) allows you to achieve a 2-layer PCB design straight out of the box.

One common PCB design challenge is how to separate the noisy digital from sensitive analog circuits including PCB traces. The TPS23861 partitions the analog port circuits at the bottom while the digital and power pins are located at the top. This allows easier partitioning of the analog and digital circuits with associated traces.

TPS23861 supports 2-layer PCBs in low to high port count systems using either mother/daughter or single board designs. In general, a single board PSE system will contain much more than the TPS23861 circuits and have a higher layer count. A daughter board based PSE system (similar to TPS23861EVM-612) partitions the higher layer count motherboard and lower cost, 2 layer daughterboard. If the daughterboard is copied many times within the system then the overall cost can benefit from the higher volumes. A high level comparison of daughterboard (based on the TPS23861EVM-613 daughterboard PCB) cost is shown in Table 1. 

Table 1. Relative Daughterboard Cost vs. Number of Layers

Number of Daughterboard Layers

Relative Single Lot Cost

2

1x

4

1.8x

6

2x

An example 2-layer PCB layout for TPS23861 is shown in graphic 1. 

Graphic 1:  TPS23861 Daughterboard PCB Layout

Each TPS23861 port uses three signals (GATE, SENSE, and DRAIN) and these signals are grouped and distributed towards the bottom end of the IC for easy connection to the supporting devices. The left and right port pairs employ a Kelvin sense ground pin for superior current sensing accuracy on the low side of the current sense resistor.

In summary, the TPS23861 provides both the pin out and collateral, including the TPS23861EVM-612, so that new designs can very simply copy and paste the existing design into the end product. Both of these contribute greatly to a low cost end product and lower design cycle time.